The requirements made of wire-free communication devices, for example mobile radio telephones, notebooks or so-called PDAs (Personal Digital Assistants), continue to rise with regard to their data transmission rate and flexibility. By way of example, the communication devices, in particular cordless or mobile telephones, and the transceiver circuits implemented therein have to be equipped for a wide variety of mobile radio standards. Examples of such mobile radio standards are GSM, UMTS/WCDMA, GPRS, GPS, Bluetooth and WLAN. The mobile radio standards cited here provide fixedly defined transmission and reception frequencies for the data transmission.
The range of said transmission and reception frequencies lies between 810 MHz in the case of the mobile radio standard GSM and 2.4 or even 5.4 GHz in the case of the mobile radio standards WLAN and 802.11. In addition, the transmission and reception frequencies used in part differ regionally. This has led in the past, for example, to the development of triple band devices which can be used both in Europe and in North America. In order to be able to satisfy the rising requirements, consideration has been given recently to the use of software-based radio transmission systems, so-called software defined radios. In these systems, a large part of the signal processing is effected by means of software and only the actual conversion to the transmission signal is performed by hardware. The advantage of these systems resides in the high flexibility with regard to the application of already existing mobile radio standards or mobile radio standards that are still being developed.
In addition to the different mobile radio standards, further different operating modes, for example simultaneous reception of a plurality of channels, monitoring of the signal quality, heterodyne reception or diversity mode (reception of the same signal on a plurality of antennas), are demanded for the transceiver. This results in an extensive and highly complex construction with different circuits for signal generation and signal processing. This causes costs and increases the space requirement.